About JSON File Validator
JSON File Validator checks whether a file contains well-formed JSON and reports its shape in one glance. Choose a file and the tool reads it as text and passes it through the JSON parser, returning a check line with the top-level type and a key count when it is valid, or a cross line with the parse error when it is not.
The valid output tells you whether the top level is an object or an array and how many keys it holds. A file containing an object with two fields reports Top-level: object and Keys: 2, while a top-level array reports its length as the key count. If no file is chosen the tool returns Choose a file.
The scope is deliberately limited to syntax. There is no schema, no type validation and no duplicate-key detection, so a file that parses cleanly is reported valid regardless of whether it contains the data you expected. The whole file is read into memory as one string, and the only error detail shown is whatever the parser reports.
How to use JSON File Validator
- 1 Choose the JSON file you want to validate.
- 2 Run the tool to read the top-level type and key count, or the parse error.
- 3 Use the message to locate and fix any syntax problem in the file.
Frequently asked questions
What does the valid result show?
A check line, then the top-level type - object or array - and a key count. The count uses Object.keys, so a top-level array reports its length as the number of keys.
Does it check the file against a schema?
No. It only validates JSON syntax. There is no schema, no type check and no duplicate-key detection, so a file that parses cleanly is reported valid regardless of its contents.
Why does the key count ignore nested fields?
The count is shallow, using Object.keys on the top level only. Nested objects inside are not counted, so the number describes the outer structure rather than the whole file.
What happens with a very large file?
The file is read entirely into memory as one string, so a very large file may be slow or fail. There is no size limit and no streaming, and the error shown is whatever the parser reports.
Free, online, and private
Free to use
JSON File Validator is completely free. There is no account to create, no login, and no hidden charge or usage limit.
Runs online in your browser
It is a free online tool that runs entirely in your browser. Nothing to download or install — open the page and start using it right away.
Your data stays private
All processing happens locally on your device. Your input is never uploaded, stored, or tracked, so it never leaves your browser.
How JSON File Validator behaves in detail
These are the specifics of this implementation — the exact ranges, defaults and fixed settings you are working with.
| Parameter | Value |
|---|---|
| Input | a single file picker, with no other fields |
| Output | for valid JSON, a check line followed by the top-level type and a key count; for invalid JSON, a cross line with the parse error |
| No file | with no file chosen the tool returns Choose a file |
| Top-level | the top-level value is reported as either object or array |
| Key count | the count uses Object.keys, so a top-level array reports its length as the key count |
| Method | the whole file is read as text and passed through JSON.parse |
Compiled from the implementation of this tool and checked against it by itoolnet.
What JSON File Validator does not do
Knowing the edges of a tool saves more time than another list of its features. These are the cases where it will not do what you might expect.
- It validates syntax only. There is no schema check, no type validation, no duplicate-key detection and no size limit, so a file that parses cleanly is reported valid regardless of whether it contains the data you expected.
- The key count is shallow. Only the top-level keys are counted - for an array that number is its length, and nested objects inside are ignored entirely, which can mislead a reader into thinking the whole structure was inspected.
- The file is read entirely into memory as a string, so a very large file may be slow or fail, and the only error detail shown is whatever the parser reports - there is no custom line and column readout.
Tested and documented by itoolnet, the team that builds and maintains this site.